The invention in particular relates to an apparatus and method operating on the line-scan principle, in which three dimensional objects are caused to move through a scanning zone and imaging information collected. This principle is widely employed for example without limitation in the security industry, to scan objects where it is desirable to gain information about their internal contents, and in medical imaging, imaging for quality control purposes or the purposes of determining the integrity of the structure, or the like.
Imaging apparatus which employs the line-scan principle is well known. Typically, such apparatus will consist of an x-ray source, the beam of which may be collimated into a curtain, usually referred to as a “curtain beam”, and is then detected by a linear array detector for example comprising a linear photodiode array. Image information is obtained by having the object of interest move linearly for example at right angles with respect to the beam and storing successive scans of x-ray transmission information derived from the linear array from which a complete image frame can be compiled.
If the object being scanned is heterogeneously transmissive of x-ray radiation, and for example consists of or contains multiple smaller objects and/or components of dissimilar materials, it can be possible to build up an image of the object, and in a particular case of the contents or components. The image may then be displayed on a viewing screen. This image can be useful for example in relation to the possible applications outlined above. In particular, it can be useful in determining the contents of a container or the internal structure of an object or body.
Even so, the image generated by such an x-ray apparatus is limited. At best it constitutes a two dimensional shadowgraph of the object being imaged. This can make it difficult to interpret.
European Patent No. 0610084 describes a method of creating a “2.5D” solid model picture for viewing. A stereoscopic pair of x-ray images is obtained using two diverging curtain beams derived from an x-ray source. These are separated into conjugate slices and the 2.5D image built up from the resulting slice information.
The resultant image is not strictly a three dimensional image (although it is often so referred to) since it is presented on a two dimensional screen rather than by means of full stereoscopic apparatus. Such a 2.5D representation in fact contains psychological cues to depth such as linear perspective, interposition, shading and shadowing rather than the full physiological depth cue known as binocular parallax or stereoscopy which is required for a full three dimensional image.
UK Patent Nos. 2329817 and 2360685 are examples of methods and systems which can be used to produce full stereoscopic image pairs. They derive ultimately from principles set out in European Patent No 0261984. In particular they are subject to the condition set out at column 4 lines 31 to 48 therein which imposes considerable constraints on detector and source beam geometry. Although stereoscopic imaging can be a relatively powerful technique, exploiting full physiological cues in relation to depth information, and thus offering the potential for a user of the x-ray apparatus to identify objects or components much more readily and clearly, it can be complex in practical operation. To exploit the stereoscopic effect, it is necessary for the observer to receive different images at each eye simultaneously. This will necessitate the use of special apparatus. Moreover, a full stereoscopic technique requires precise control of the image collection process having regard to the conditions identified above. If the stereoscopic pair is to be effective, the respective images must be collected with a parallax that closely approximates to that which would be tolerated by the observer's eyes. For these reasons, full stereoscopic imaging has not gained wide acceptance for scanning machines of this type.
Some of these problems are mitigated by PCT publication WO2008/119967 in which the line-scan principle is used to generate successive images as relative movement is effected along a single linear axis between an object and a source/detector arrangement so as to display the monocular movement parallax between such successive images and offer some further three-dimensional cues.
The line-scan x-ray technique might find application in relation to imaging for medical or other investigative examination purposes, quality control etc where it is desirable to view a multi-component target object. A better resolution of the exact shape and location of components of objects in three-dimensional space would be a considerable improvement on present techniques, especially if composition could also better be characterised.